The most important function of red cell hemoglobin is to bind oxygen at the lungs, carry it in blood and release a sufficient amount at the tissues. This research proposal is designed to study the intramolecular regulatory mechanism of oxygen binding and release by human hemoglobin under various experimental, physiological, and pathological conditions. Varieties of synthetic hemoglobins containing hemes with chemically modified side chains at different positions of the porphyrin ring will be prepared. Detailed studies on the structural and functional properties of these synthetic hemoglobins will provide us with important information about the electronic and steric effect of the modifications near the heme on the ligand binding properties of hemoglobin. The structural-functional relationship in abnormal hemoglobins with a mutation site near the heme pocket will also be studied by probe techniques including the heme-spin-label method and 13C or 15N-NMR spectroscopy. The latter experiments will be performed after preparation of hemoglobin containing 13C or 15N enriched heme. To correlate these studies with clinical problems due to decreased oxygen transport in various disorders, the relationship between oxygen equilibrium curves of blood and the clinical status of patients will be studied particularly in those who require blood transfusion. The effect of transfusion of red blood cells containing different amounts of DPG or IHP on the efficiency of tissue oxygenation will also be investigated.